A wet type developing device of the electrographic printer is disclosed in JP 2012-68372 A.
This wet type developing device comprises, a developing roller in contact with a surface of a photoconductor drum, and an anilox roller (convexo-concave roller) in contact with a surface of the developing roller and in part of its surface immersed in a liquid toner. The developing roller and the anilox roller are driven to rotate so that the liquid toner is supplied onto the surface of the developing roller via the anilox roller, the developing roller develops an electrostatic latent image formed on the surface of the photoconductor drum with the liquid toner which was supplied.
The anilox roller of the wet type developing device which comprises the anilox roller and the developing roller is as follows.
The anilox roller has cells (recesses) formed on its surface and rotates to convey the liquid toner filled in the cells so that the filled liquid toner is delivered to the surface of the developing roller.
Because an extra liquid toner overflowed from the cells then exists on the surface of the anilox roller, a regulation blade is made to come in contact with the surface of the anilox roller to scrape off the extra liquid toner, so that thickness of a liquid toner layer is uniformized and thereby a liquid toner supply to the surface of the developing roller, i.e. a liquid toner supply to upstream side of the region of contact between the surfaces of the anilox roller and the developing roller is regulated.
Anilox roller is a metal cylinder whose surface is formed with cells by corrosion or a machine sculpture and afterward plated with hard chrome or coated with ceramics to raise wear resistance of the surface.
A regulation roller blade to scrape the extra liquid toner from the surface of the anilox roller is a thin metal blade contacting on the surface of the anilox roller
Therefore, the regulation blade is worn early. When the regulation blade is worn, on the surface of the anilox roller, a linear scratch may occur by the worn regulation blade. An unevenness occurs to the liquid toner to be supplied to the surface of the developing roller because of the linear scratch, so that the electrostatic latent image on the surface of the photoconductor drum cannot be developed definitely, hence the worn regulation blade is changed. In other words, the regulation blade is expendable supplies.
In addition, the regulation blade is adjusted to uniformly contact on the surface of the anilox roller so that thickness of the liquid toner layer on the surface of the anilox roller is uniformized. For example, an edge (ridge line) of the tip of the regulation blade is adjusted to be accurately pressed to the predetermined position of the surface of the anilox roller by uniform power.
The developing roller of the wet type developing device which comprises the anilox roller and the developing roller is as follows.
The liquid toner layer of uniform thickness is formed on the surface of the developing roller with the liquid toner supplied by the anilox roller. The liquid toner of this liquid toner layer is transferred to an electrostatic latent image on the surface of the photoconductor drum and develops the electrostatic latent image.
At this time the liquid toner which was not transferred to the electrostatic latent image on the surface of the photoconductor drum is left on the surface of the developing roller as a residual liquid toner. Therefore, a history of the electrostatic latent image is left on the surface of the developing roller. In other words, one part with the liquid toner and the other part with no liquid toner occur on the surface of the developing roller. This history of the electrostatic latent image will be an obstacle to the formation of the liquid toner layer of uniform thickness before developing on the surface of the developing roller.
Therefore, the history of the electrostatic latent image is erased by bringing a cleaning blade into contact with the surface of the developing roller and scraping the residual liquid toner off the surface with the cleaning blade after transferring the liquid toner from the developing roller to the photoconductor drum.
The developing roller is a metal cylinder whose surface is coated with a rubber having elasticity and electrical conductivity. Therefore, a cleaning blade to scrape a residual liquid toner off the surface of the developing roller is made of urethane. For example, the cleaning blade is made with a metal plate whose tip an urethane board is bonded to.
However, the surface of the developing roller may be damaged by abrasion of the cleaning blade in itself even though the cleaning blade is made of urethane. Because the electrostatic latent image on the surface of the photoconductor drum cannot be definitely developed where the surface of the developing roller is damaged, the worn cleaning blade is changed. In other words, the cleaning blade is expendable supplies.
In addition, the cleaning blade is adjusted to uniformly contact on the surface of the developing roller so as to surely scrape off the residual liquid toner on the surface of the developing roller. For example, an edge of the tip of the cleaning blade is adjusted to be accurately pressed to the predetermined position of the surface of the developing roller.
As described above, the conventional wet type developing device comprises the regulation blade to regulate a liquid toner supply by the anilox roller to upstream side of the region of contact between the surfaces of the anilox roller and the developing roller and the cleaning blade to erase a history of the electrostatic latent image on the surface of the developing roller.
Because both the regulation blade and cleaning blade are worn early and damage the surfaces of the anilox roller and the developing roller, respectively by being worn, it is necessary to change them frequently.
Therefore, since it is necessary to produce a lot of two kinds of blades different in use, material and shape and to keep them, the production cost of the blades is high, and the safekeeping of the blades is troublesome.
In addition, the regulation blade is adjusted to uniformly contact on the surface of the anilox roller and the cleaning blade is adjusted to uniformly contact on the surface of the developing roller.
Therefore, these two blades must be separately adjusted, and these adjustment works of the blades are troublesome because these adjustment works are difficult.
In addition, given a deflection of the regulation blade, the holder to attach the regulation blade becomes a thick and big part, and thus the compactification of the device is difficult.
Further, the cleaning blade may not erase the history of the electrostatic latent image on the surface of the developing roller surely due to a phenomenon called caking that a highly-concentrated liquid toner coagulates on the cleaning blade separately from abrasion of the cleaning blade in itself.
Furthermore, the developing roller and the cleaning blade are strictly required to have a smoothness of the surface of the developing roller and a straightness of the edge of the cleaning blade, respectively in order to surely erase the history of the electrostatic latent image on the surface of the developing roller.
Therefore, a high formation technology and an abrasion technology are necessary for the production of the developing roller and the cleaning blade and, as a result, lead to an increase in cost.
In addition, a nip pool of liquid toner (a state that liquid toners are collected) may occur in a portion on the anilox roller upstream of the part in which the surfaces of the anilox roller and the developing roller are in contact with one another even though the regulation blade and the cleaning blade are accurately exactly adjusted as described above. In this case, the quantity of the liquid toner on the surface of the developing roller before the final developing will be fixed after the surface of the anilox roller comes in contact with the surface of the developing roller, but the supply precision of appropriate and uniform amount of the liquid toner to the surface of the developing roller may decrease gradually while a liquid toner adheres and deposits in the cell of the anilox roller.
In view of the problems mentioned above, it is an object of the present invention to provide a wet type developing device whereby the regulation of a liquid toner supply by the anilox roller to upstream side of the region of contact between the surfaces of the anilox roller and the developing roller and the erasure of a history of the electrostatic latent image on the surface of the developing roller can be performed with the same roller, the surfaces of the anilox roller and the developing roller are not injured even though the roller is worn, the production cost of the roller is low, the safekeeping of the roller is easy, the adjustment work of the roller is easy, and the production of the developing roller is easy.